Several diseases of prematurity are thought to be related to oxidative injury and many of the available markers are unsatisfactory. An assay was developed using HPLC with electrochemical detection for the quantitation of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) as a proposed indicator for oxygen-derived free radical injury to DNA in preterm infants. A median value of 3.79 micromol/mol creatinine was obtained for normal children (2-15 years old, n=14). Urinary 8-OHdG excretion in neonates ranged from 0-99 micromol/mol creatinine. There were no gestation or birthweight related differences in urinary 8-OHdG, and no correlation with urinary malondialdehyde. Mean 8-OHdG excretion increased with postnatal age (r=0.80, p < 0.0001, n=15), mirroring the growth velocity curve. These changes could also be due to changes in the activity of the enzyme responsible for 8-OHdG excision. Urinary 8-OHdG levels are unlikely to accurately reflect oxygen derived free radical activity given the strength of the relationship with growth.